The present invention concerns a gas discharging type display panel, such as a plasma display panel, and a display device therefor, and, particularly, it relates to a gas discharging type display panel and a display device therefor, which is capable of easily selecting a display cell and which has an improved working life.
Since a gas discharging type display device, such as a plasma display device produces a display by self light emission, its view angle is wide and the display is easy to see. In addition, it has the advantageous feature that it is capable of being prepared as a reduced thickness type device or of attaining a large area screen, and so the application thereof to display devices for information terminal equipment and high quality television receiver sets already has been started. The plasma display is generally classified into a DC driving type and an AC driving type. Of the two types, the AC driving type plasma display attains a high brightness by use of the memory effect of a dielectric layer covering the electrodes and can obtain a practical working life by the formation of a protection layer and the like. As a result, the plasma display has been put to practical use as a multi-purpose video monitor. An example is shown in FIG. 22 and FIG. 23. FIG. 22 is a perspective view illustrating the structure of a plasma display panel which has been put to practical use. In the figure, a front substrate 1 is illustrated as being spaced from a back substrate 2 and a discharging space region 3 for the sake of easy understanding. The front substrate 1 has a structure in which display electrodes 6 made of a transparent conductive material, such as ITO (Indium Tin Oxide) or tin oxide (SnO2), bus electrodes 7 made of a low resistance material, a dielectric layer 8 made of a transparent insulating material and a protection layer 9 made of a material, such as magnesium oxide (MgO), are formed on a front glass substrate 4. The back substrate 2 has a structure in which address electrodes 10, barrier ribs 11 and a fluorescent layer 12 are formed on a back glass substrate 5. Then, a discharging space region 3 is formed between the front substrate 1 and the back substrate 2 by appending the front substrate 1 and the back substrate 2 such that the display electrodes 6 and the address electrodes 10 are substantially perpendicular to each other.
FIGS. 23(a) to 23(c) are cross sectional views of the gas discharging type display device shown in FIG. 22. FIG. 23(a) shows a cross section in parallel with the address electrodes 10, FIG. 23(b) shows a cross section taken along line A-B in FIG. 23(a) vertical to the address electrodes 10 and FIG. 23(c) shows a cross section along line C-D in FIG. 23(a) vertical to the address electrodes 10. In the gas discharging type display device illustrated herein, an address discharge is generated by applying a voltage between a pair of display electrodes 6 disposed on the substrate 1 and the address electrodes 10 disposed on the back electrode 2 to select a predetermined cell, and a main discharge is generated by applying an AC voltage (pulse voltage) between the pair of display electrodes 6. Ultraviolet rays generated by the main discharge excite the fluorescent body 12 to emit light, thereby producing a display.
An example of the standard gas discharging type display device illustrated herein is described, for example, in Flat Panel Display, 1996 (edited by Nikkei Microdevice, 1995) from page 208 to page 215.
In the publication described above, an address discharge for selecting the display cell is conducted between the display electrodes 6 disposed on the front substrate 1 and the address electrode 10 disposed on the back substrate 2. In this case, since the distance between the display electrode 6 and the address electrode 10 is as large as about 0.2 mm, an application voltage required for generating an address discharge (referred to as address voltage) is at a high value of 200 V or higher. In the arrangement disclosed in the publication, for lowering the address voltage, a high voltage of about 300 V is applied to an electrode 62 on the side of a common electrode of the display electrode 6 (referred to as an auxiliary discharge) and then an address discharge is generated at a predetermined display cell. That is, the address voltage is set lower by generating an auxiliary discharge in all of the display cells and forming wall discharges on the surface of the protection layer 9 covering the display electrode 6 and the fluorescent layer 12 covering the address electrode 10.
On the other hand, the distance between the display electrodes 6 and the address electrodes 10 may be shortened for lowering the address voltage. However, if the gap between the front substrate and the back substrate is merely narrowed, this is not preferred, since the discharging space is also reduced. Further, if the gap between the front substrate and the back substrate is narrowed, since the fluorescent layer 12 on the address electrode 10 is brought closer to the display electrode 6, excess erroneous emission of the fluorescent layer is increased upon generating of the auxiliary discharge or address discharge at the display electrodes, or degradation of the fluorescent layer by plasma damage is caused.
In addition, the gas discharging display device disclosed in the above-mentioned publication involves the following problems. (1) For generating the auxiliary discharge for forming the wall charges described above, a time is required for forming the wall charges, which shortens the display time and makes it difficult to provide gradation in the display. (2) Since the fluorescent layer 12 is present on the address electrodes 10, the fluorescent layer 12 emits light erroneously upon address discharge. Therefore, the contrast on the display screen is lowered. (3) Since the fluorescent layer 12 is present on the address electrodes 10, the fluorescent layer suffers from plasma (ion) damage due to the address discharge. This causes a shortening of the working life of the gas discharging type display device.
Each of these problems results from the fundamental structure of the gas discharging type display device. That is, these problems are caused due to the arrangement of the address electrodes, barrier ribs and the fluorescent layer as shown in FIG. 22 and FIGS. 23(a) to 23(c).
Further, in a case of manufacturing this gas discharging display device, a problem exists in a step of forming the barrier ribs 11 on the back substrate 2.
For example, in the barrier rib formation using a thick-film printing process, since thick film printing and drying are repeated over and over, this tends to cause, for example, defects in the dimensional accuracy of a thick film pattern, alignment failure between each of thick film patterns or deformation of a large screen plate. Therefore, the manufacturing process is lengthened and the manufacturing yield is lowered. Further, it is difficult to obtain a refinement to about 0.05 mm using the thick-film printing process, tending to cause more deformation in a larger screen plate. This brings about a difficulty in the refinement and the size-enlargement of a display screen.
Further, for formation of barrier ribs, a photo-burying method, a sand blasting method and a photosensitive paste method have been proposed and are being studied. However, they have the following problems, respectively.
The photo-burying method comprises forming a rib-shaped groove pattern on the back substrate 4, formed with address electrodes 10, by using a light sensitive film and burying a barrier rib layer in the groove pattern. With this method, it is difficult to form a groove pattern having a depth of 0.1 mm or more at a width of about 0.05 mm. In addition, it is an important to assure chemical stability between the barrier rib layer to be buried and the light sensitive film (solution or reaction) and to develop an effective method of burying the barrier rib material.
The sand blasting method comprises forming a barrier rib pattern by a light sensitive film on a barrier rib layer disposed on the back glass substrate 5 formed with address electrodes 10 and removing the barrier rib layer from a region in which the light sensitive film is not present by using sand blasting. Also in this a method, it is necessary to repeat printing and drying for obtaining a thick barrier rib layer, since the thickness of the barrier layer that can be printed in one step is small. Further, there is a requirement for covering the address electrode with other material in order to protect the address electrode 10 against damages which might occur in the sand blasting step. That is, the sand blasting method also involves a problem that the step is lengthened and there is a concern for possible damage to the address electrode, and it is also important to develop a light sensitive film which is inexpensive and has excellent resistance to blasting in order to lower the manufacturing cost of the gas discharging type display device.
The light sensitive paste method comprises forming a barrier rib layer by using a light sensitive barrier rib material and forming barrier ribs by well-known photolithography, such as exposure and development. While this method is a simple process, development of the material has not yet been completed. Therefore, the limit for fabrication and the limit for the lamination are unknown if the thickness is increased. Also for the film forming method, a thick-film forming technology has not yet been established, which is a technique yet to be developed in the future.
As described above, each of the prior art stated above is a technique for forming barrier ribs of different material on the back substrate, so that the manufacturing step is lengthened and it is difficult to obtain a high manufacturing yield.
Further, in the method of forming the barrier ribs described above, barrier ribs are obtained by forming a barrier rib layer on the back substrate formed with the address electrodes and then sintering them. Therefore, since the sintering temperature for the barrier ribs is higher than the distortion point of soda lime glass used for the back glass substrate 5, this also brings about a problem of glass deformation. Further, if the area of the display screen is increased, there may also be a problem of barrier rib shrinkage due to sintering. These problems lower the manufacturing yield of the gas discharging type display device.